I am facing the same "issue" for my tanks. 3 weeks away (far, far away).
I am not concerned about the fishies. They will do just fine without food for this time. Shrimps of course too. Autofeeders and those slow dissolving food discs can do a lot of harm.
I am concerned about temperature. I don't have air condition, and it can get a little warm. I am planning to raise up the canopies for better airflow.
I am concerned about power outages. These will screw with your mechanical timers and result in a shift of lighting periods. I am planning to buy electronic timers with backup batteries.
I autodose all my tanks daily (14 day period before refilling bottles). I will set them to dose only every other day. At the same time, I will reduce lighting (take out some fluorescents, and/or reduce lighting period).
If I were you, I would look into autodosing. Pretty easy with a powerhead, some tubing, and a timer, search for autodosing, I posted some pics and explanations.
Since you can not take out a bulb, you can either hang them higher, and/or reduce the lighting period, say to 6 hours instead of 10. That will slow things down, along with reduced fertilizer dosing.
On the other hand, if you get someone to dose once a week, or if you dose nothing for 3 weeks, it might still come out to the same. Autodosing is still good because you don't have to dose every day which can become a drag.
One worries too much.